Mechanism of contractile response to bombesin of the longitudinal muscle from guinea pig ileum.
The mechanism of action of bombesin in the longitudinal muscle with myenteric plexus (LM-MP) preparation from guinea pig ileum was examined. Bombesin (3 x 10(-10) to 3 X 10(-7) M) induced contraction in a concentration-dependent manner. The contractions induced by bombesin at concentrations of 10(-9) M and less were tetrodotoxin- and scopolamine-sensitive, and those induced at concentrations of 10(-8) M and greater were tetrodotoxin-sensitive, and partially scopolamine-sensitive. In association with the mechanical response to bombesin, the peptide induced Ca(++)-dependent and tetrodotoxin-sensitive release of acetylcholine from the LM-MP preparation. Bicuculine inhibited partly both the cholinergic contraction and the release of acetylcholine induced by bombesin, suggesting the involvement of a gamma-aminobutyric acid (GABA)-ergic mechanism. Bombesin also induced Ca(++)-dependent and tetrodotoxin-sensitive release of endogenous and [3H]GABA from the LM-MP preparation. These results indicate that bombesin induces contraction mainly mediated mediated by cholinergic and partially mediated by noncholinergic excitatory neurons. GABAergic neurons may be involved in a part of the response to bombesin mediated by the cholinergic neuron.
Takeda
K
K
Department of Pharmacology, Kobe University School of Medicine, Japan.
Taniyama
K
K
Saitoh
Y
Y
Tanaka
C
C
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001839:Bombesin / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D005680:gamma-Aminobutyric Acid; D000109:Acetylcholine; D001839:Bombesin; D001640:Bicuculline